Electroacoustic tone modifying systems for stringed musical instruments



March 12, 1963 c. R. EVANS 3,080,785

ELEcTRoAcousTIC TONE MODIFYING SYSTEMS FOR Y STRINGED MUSICAL INSTRUMENTS Filed Aug. 25, 1958 5 Sheets-Sheet l xu. v

C. R. EVANS March 12, 1963 3,080,785 ELECTROACOUSTIC TONE MODIEYING SYSTEMS FOR STRINGED MUSICAL INSTRUMENTS Filed Aug. 25, 1958 5 Sheets-Sheet 2 @IMM March l2, 1963 c R EVANS 3,080,785

ELECTROACOUSTIC TOME MODTFYTNG SYSTEMS FOR STRINGED MUSICAL INSTRUMENTS Filed Aug. 25, 1958 5 Sheets-Sheet 5 y MSLWW@ gr-l March 12, 1963 c. R. EVANS 3,080,785

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March l2, 1963 c. R. EVANS 3,080,785

ELECTROACOUSTIC TONE MODIFYING SYSTEMS FOR STRINGED MUSICAL INSTRUMENTS Filed Aug. 25, 1958 5 Sheets-Sheet 5 7mm/7 MPa/75? United States Patent Office 3,080,785 Patented Mar. 12, 1963 3 080 785 ELECTROACOUSTIC TGN MGDIFYING SYSTEMS FR STRINGED MUSECAL INSTRUMENTS Chauncey Richard Evans, Salt Lake City, Utah, assigner, by mesne assignments, to Atnk Corporation, Sait Lake City, Utah, a corporation of Utah Filed Aug. 25, 1958, Ser. No. 756,950 1 Claim. (Cl. SLi- 1.16)

lThis invention relates to electroacoustic systems and more particularlyv to systems in which the output of an electromechanical energy transducer is modified in various ways to produce certain predetermined acoustic eects which are deemed pleasing and desirable.

Musical instruments of the string family have long been noted for the tonal beauty and intimate quality of their music. The musical tones in these instruments are produced by an acoustic resonator or tone chamber which is energized by the vibrations of strings activated by the performer. The quality or characteristics of the music thus produced is determined by the design of the acoustic resonator which forms the tone, and consequently, this element of the instrument is usually regarded as being the most critical in design. Master craftsmen such as Stradivari, Amati, and Guarneri produced instruments of such rare tonal beauty as to become famous throughout the world.

With the present day advent of electronics, various attempt-s have been made to produce stringed instruments having improved tonal characteristics and higher levels of sound intensity. A conventional electromechanical or electromagnetic sound transducer, used in conjunction with a vacuum tube amplifier and loudspeaker, is capable of giving any level of sound intensity desired, but the tonal quality of such instruments cannot compare with those of the old world craftsmen. This is undoubtedly due to the fact that a faithful reproduction of the vibratory frequencies of the strings will not necessarily produce musical -sounds having the desired characteristics.`

The lbeautiful tones which emanate from the acoustic instruments made by these master craftsmen are the result of the string vibrations plus the modulation and added overtones introduced by the acoustic resonator. With this fact in mind, it is readily seen that, in order to duplicate orimprove upon these acoustic instruments in an electroacoustic device, it is necessary either to provide a system capable of modifying and introducing certain desired characteristics into the electrical output from the vibrating strings, or capable of modifying, in a predetermined manner, the acoustic energy produced by the loudspeaker, or capable of doing both.

Accordingly, it is an object of this invention to provide an improved electroacoustic system for producing music from stringed instruments.

Another object of this invention is to provide an electroacoustic system in which the musical tones produced from vibrating strings are modified in such fashion as to enhance their aesthetic effect.

Another object of the invention is to provide a novel electromechanical transducer for stringed instruments.

Another object of the invention is to provide a composite electromechanical transducer having variable frequency characteristics.

Another object of the invention is to provide an improved loudspeaker system for stringed instruments.

A further object of the invention is to pro-vide a loudspeaker system for stringed instruments in which the acoustic energy produced by the loudspeaker is enhanced by virtue of modifying the harmonic and overtone content of such energy.

A further object of the invention is to provide an improved formant circuit for modifying the waveform of an electrical signal.

A further object of the invention is to provide aportable self-contained electroacoustic instrument of the stringed variety.

A still further object of the invention is to provide a self-contained electroacoustic instrument capable of receiving radio broadcasts and enabling the instrument to be played in conjunction with such radio broadcasts.

A still further object of the invention is to provide an electroacoustic instrument requiring no physical connection with its associated loudspeaker system.

In accordance with these objects, the -system of this invention comprises an electromechanical transducer of piezoelectric material which is used as the bridge element for any conventional stringed instrument. The mechanical vibrations of the strings are translated into electrical energy which in turn may be either (l) modilied by appropriate formant circuits and reproduced through a conventional loudspeaker system, or (2) amplified in a conventional manner and reproduced through a specifically loudspeaker system to add the desired tone coloration.

This preferred embodiment of the invention, together with certain modifications thereof, is illustrated in the accompanying drawings in which:

FIG. 1 is a block diagram of the basic system of the invention;

FIG. 2 is a plan view of a classic guitar body showing the bridge element of the instant invention together with the controls therefor; f

FiG. 3 is a cross section taken along the line 3 3 of FIG. 2;

FIG. 4 is a side elevation of the guitar body;

FIG. 5 is a diagrammatic view showing the electrical connections to the bridge element;

FIG. 6 is a horizontal cross sectional view of the loudspeaker system of the present invention taken just below the top of the cabinet;

FIG. 7 is a cross section view in elevation line 7-7 of FlG. 6;

FIG. 8 is a vertical cross section with parts in side elevation of the loudspeaker system;

FIG. 9 is a cross section view in elevation taken along line 9 9 of FiG. 6;

FIG. l() is a block diagram of a formant circuit in accordance with the instant invention;

FIG. 11 is a block diagram of a self-contained musical instrument; and

FIG. l2 is a block diagram of a music system having no interconnecting wires between the instrument and loudspeaker.

The operation of the basic system of the invention may be easily understood by making reference to FIG. l of the drawings which is a block diagram of the system. The pickup transducer l, which has three separate outputs, feeds into a switcher-mixer 2 which provides the functions of selectively switching in and out all three of the pickup transducer outputs and electronically mixing the selected outputs.

The output from the switcher-mixer is fed through a preamplilier stage 3 and an amplifier stage 4 to provide the necessary increase in level, and the resulting amplified signal is fed to a loudspeaker transducer 5 which, in addition to reproducing the electrical signal, adds certain desired tonal colorations by means of a unique baming structure hereinafter described.

While the invention is adaptable to any form of string instrument, the classic guitar, a plan view of which is shown in FIG. 2, has been selected for the purpose of this description. The neck 6 of this guitar extends far enough into the body portion to enable the player to taken along properly finger the fretboard (not shown) even at its extreme end where it is joined tothe main body portion 7 of the guitar. A projection S on the guitar body provides a convenient recess 9 for support of the guitar on the players knee a-nd yet does not interfere with the lingering of the fretboard.

The guitar strings generally designated by the letter S extend over bridge member iti, as is more clearly seen from FlGS. 3 and 4.

The bridge member 10 is constructed in three tiers or layers. of piezoelectric material, preferably of a ceramic titanate such as barium titanate. layer consists of a single ceramic titanate element 17. Placed on top of element 17 and providing a zone of sep* aration is a layer 18 of resilient material having a high degree of compliance, such as neoprene. The second transducer layer comprises two ceramic titanate members i9 .and 20, and on top of these members is located a second layer of high compliance material such as neo` prene.

The top layer of the transducer is comprised of six individual ceramic titanate elements 11 through 16, each of which has a string of the instrument mounted thereon.

The individual transducer elements of the various layers, while different in shape, are all similar in construction. Each element is constructed of the sameY material, barium titanate, and has its top and bottom faces metalized with a suitable plating to provide means for making electrical contact therewith. K

FIG. is a diagrammatic view of the electrical connections to the bridge member, showing the polarity observed in connecting tothe individual transducer members. A separate output is taken from each transducer layer and each transducer layer is ldesigned to have a different frequency response characteristic so that by selective switching and mixing in the switcher-mixer 2, an endless variety can be obtained in the response characteristics of the bridge output.

In contrast to the conventional acoustic instrument which requires a Carefully designed resonatorbody, the body 7 of the classical guitar shown in FIG. 2 serves no purpose other than the conventional one of providing support for the strings, etc., and in no way contributes to the tone quality. 'The output of the instrument is derived. solely from the bridge. transducer 1i?. For this reason, it is possibleto fabricate the guitar body by such Ysimple techniques as molding, and the body itself may be switch in. and out the three separatelayers of the bridge,

transducer` it? and also controlrthe amplitude ofthe individual outputs. Y

The switcher-mixer 2, preampliiier 3, and power amplifier 4, may be of any conventional design wellknown in the art, which is adapted for the particular requirements of the instrument involved. Y i

The construction of the loudspeaker system of the instant invention is'seen by making reference to FiGS.V 6

through 9 of the drawings. VThe enclosure 25 lwhich is generally" rectangular through anyv cross section contains three loudspeakers, 26, 27, 28, securely mounted onbaftiboard 29 which divides the enclosure into two compartf ments, 30 and '31. As seenfromiPiG. 9, the only openings in the bafrleboard' 29 are'the three cut-outs for the sr'geakers,V 26, 27, and 28.' f i Mounted in compartment 31,' on a second baieboard 32,'.which isrectangular in shape asshown inAFIG. 7,v is

jadiaph'ragm assembly generally designated by the nu meral $3. This diaphragm'assembly is of a construction The bottom transducer ture is well known in the iield of drums and forms no part of this invention, it is not believed .necessary to describe its construction in detail.

in mounting the diaphragm assembly 33 on the battleboard 32, a cut-out is provided in the baiileboard 32 of va diameter slightly smaller than the diaphragm assembly 33, and the assembly 33 is'mounted in spaced relation to the batileboard 32 in .such a manner that a small circumferential slot 35 is provided Vbetween the assembly 33 and the baiiieboard 32. The composite structure thus produced is mountedV on. the baieboard 29 and spaced therefrom by spacer members 36. The rear of compartment 3l behind the diaphragm assembly 33 is left open.

Mounted in the compartment 39 on the baffleboard 37 which forms the front of the enclosure 25 is a pair of diaphragm assemblies LS and 39 which are similar in construction to the assembly 33 previously described. r1the yassemblies 38 and 39 are spaced from the batileboard 37 by circumferential slots dit and 41. Spacer members 42 extendbetween the baiileboards 29 and 37 to add rigidity to 'the structure and to additionally serve the purpose or" preventing undesired resonances from occurring in the compartment 30.

To further improve the frequency response of compartment 30, a series ofterraces 4153, d4, are provided in builtup fashion on the face of the baiileboard 29. lt will be understood by anyone skilled in the art that variations in the `response characteristics Vof therenclosure can be effected by changing the volume of the enclosure and the relative locations and dimensions of the diaphragms and ba'iieboards. The important consideration inrany modification is that the 4diaphragm and loudspeakers remain in acoustically coupled relation.

The loudspeaker system thus described has important differences over conventional so-called high iidelity enclosures is not to give a faithful acoustic reproduction of the original electric signal, but rather to add certain tone colorations to the acousticcnergy developed by the loudspeakers. This eifect is achieved by virtue of the diaphragm assemblies and their mounting.

Each of the diaphragm .assemblies is chosen to resonatey at a different frequency, and these frequencies are selected to reinforce certain desired fundamental tones and provduce modulations of the high overtones with lthe funda- Excitation of the diaphragms occurs with each Vintona-V tion of the Ystrings regardless of the resonant frequency of the diaphragm and the efect thus produced greatly enhances the beauty of the generated tone. For example, when the high frequency stringsqare vibrated, the dia- Vphragrns tuned to ylower frequencies will'be excited and similar to conventional drumheads and consistsqof a tiex,`

ible diaphragm 34 held in taut condition by conventional mounting rings and tightening assembly. Since such structhen decay in transient fashion to produce a head or intonation effect on the high frequency tones. This in'- ing no diaphragm assemblies.V

rrthe tone variations thus producedrare found to beV most plcasantand'are superior to those produced by a Y conventional loudspeaker system. i i It will -be realized by thoseskilledin the artthat it is possible to accomplish electrically what the loudspeaker tional loudspeaker to give-the desired result. q

The incoming signal isfed to aseries of ilters d5, 46,

4.7, which Vare designed topassVV thevlow frequencies, highn frequencies, and middle frequencies, respectively. The middle frequencies are amplied by amplifier d8 and further amplified by amplifier 49, and reproduced by the loudspeaker system Without having their waveform electrically modiiied in any fashion. The high and lov frequencies are fed into modulator 50, Where thehigh overtones are modulated by the fundamental frequencies, and the resulting signal is amplified by ampliier 51 and fed to a `series of shock-excited oscillators 52 through 57. These oscillators are tuned to separate frequencies in the high and low bands and adjusted in such manner that when shocked, the oscillator produces a damped oscillation at the frequency to which it is tuned. The duration of this damped oscillation may be varied to produce the result desired. The outputs of each of these shockexcited oscillations, together with the unaltered middle frequency band, is fed to the loudspeaker system, and the result pro-duced is most pleasant.

To create additional eiiects, an artificial overtone generator 58 may be provided to mix with the high frequencies from filter 46 in mixer 59 before modulating with the low frequencies in modulator 50.

FIG. 11 is a block diagram of a musical instrument incorporating a broadcast tuner such that the transducer bridge output may be mixed with the broadcast signal and the resultant acuostic eiiect be that of actually performing with the regular broadcast. This embodiment is made pos-sible by the use of transistors and other miniaturized components. An additional input is added t0 the mixer switcher to mix the broadcast signal and instrument signal, and the output of the mixer switcher is arnplied and reproduced by a transistor amplifier and a loudspeaker which are also contained in the instrument. The same principle explained in connection with the loudspeaker embodiment of FIGS. 6 to 9 may be employed in the self-contained instrument, although on a -rnuch reduced scale.

FlG. 12 is a block diagram of a wireless embodiment of the invention in which the musical instrument contains a transmitting oscillator, thus requiring no interconnecting cables between the instrument and the reproducing system.

The signal generated by the transmitting oscillator located in the musical instrument is received and amplilied at a remote point and reproduced through the loudspeaker system of the invention.

It will be appreciated from the above description that by means of the instant invention it is possible to achieve, 1n an inexpensive instrument, tonal qualities which formanso/rse erly have been realized only in the expensive instruments made by master craftsmen. By using a larger or smaller number of the diaphragm assemblies, it is possible to increase or decrease the variety of tonal effects available, and such variation is controlled only by the limitations of cost and space.

While the invention has been illustrated and described in certain embodiments, it is recognized that variations and changes may be made therein without departing from the invention set forth in the claim.

1 claim:

In a stringed musical instrument, the combination comprising piezoelectric transducer means for converting the energy of the vibrating strings into electrical energy; amplifier means operatively connected to said transducer means for amplifying the electrical energy; and a loudspeaker system operatively connected to said amplifier means for converting the electrical energy into acoustic energy, said loudspeaker system including an enclosure 'having a top wall, a bottom wall, opposed side walls,

and a front end wall, a vertical baleboard mounted within said enclosure to divide the enclosure into two separate compartments, said batiieboard having three ports therein, three loudspeakers mounted on said baliieboard in covering relationship with respect to said ports, said front Wall of said enclosure having two ports therein, a pair of separate auxiliary diaphragms mounted on said front wall within the enclosure and adjacent said ports in said front wall, and a third auxiliary diaphragm in said enclosure rearwardly of said loudspeakers.

References Cited in the iile of this patent UNITED STATES PATENTS 1,258,491 Sprinkle Mar. 5, 1918 1,750,069 Truett et al Mar. 11, 1930 1,841,658 Lindenberg Jan. 19, 1932 1,856,749 Desbriere May 3, 1932 1',.e-1-5,858 Miessner .lune 27, 1933 1,923,870 Kressmann Aug. 22, 1933 2,059,929 Bobb Nov. 3, 1936 2,073,071 Nernst Mar. 9, 1937 2,287,105 Kannenberg June 23, 1942 2,476,572 Wenzel July 19, 1949 2,485,751 Larsen Oct. 25, 1949 2,491,982 Kincart Dec. 20, 1949 2,550,176 Vitovsky Apr. 24, 1951 2,571,899 Kroft et al. Oct. 16, 1951 

